Various types of web or travelling sheet, flat-bed filters have been proposed. It has been customary to pump the contaminated liquid by means of a pressure pump into the upper, or contaminant chamber above the filter to generate a pressure head therein, pressing the fluid components of the contaminant through the filter. This requires seals to provide a tight joint between the inlet chamber portions and the filter paper during the filtration. The contaminant is usually pumped through an inlet conduit to this chamber, so that the pump has to handle the unfiltered contaminated fluid.
A tight seal of the housing portion of the filter which defines the contaminant chamber customarily includes sealing covers or elements which close off slits through which the filter web, typically filter paper, can be pulled for replacement thereof when the filter paper has become clogged with solids. These sealing edges or sealing covers clamp against the filter web or the support plate. The openings to be sealed preferbly are held as small as possible. The sealing mechanism usually is required only at the slits through which the paper passes since the overall filter housing can be constructed as a unitary structure, closing off the filter chamber at both longitudinal sides of the filter web. Upon application of contaminant into the contaminant chamber, under pressure, it is difficult to prevent escape of contaminant, and particularly liquid components thereof, through the slits through which the filter paper enters the filter chamber, even if the seals are tightly formed. As contaminant enters the filter chamber, the area around the seal itself is subject to caking of contaminant solids, which frequently interferes with proper sealing upon replacement of a strip of filter paper on the flat bed.
Filter structures in which the filter paper alone separates the contaminant chamber from the filtrate chamber additionally have the disadvantage that liquid components of the contaminated fluid, and carrying only a minor portion of contaminating solids, can pass around the edges of the filter paper and thus contaminate the liquid in the filtrate chamber. To prevent such bypassing of the filter paper, additional sealing arrangements are required to clamp the longitudinal edges of the filter web to portions of the housing structure defining the contaminant chamber. Those sealing edges are also subject to deposition of solids and improper sealing upon release of pressure in the contaminant chamber, and movement of the filter paper to a new portion thereof.
Structures of the previously proposed type usually use a large filtrate chamber, the bottom of which is connected to a pump or to a gravity line through which filtered fluid is removed, for example for collection in a tank and for recycling, or for disposal as filtered fluid. If a pump is provided, then it is usually of a pumping capacity to insure removal of the filtered fluid and pumping thereof into a storage or further disposal tank.
It has already been proposed to temporarily clamp the edges of a web of filter paper in a vertically movable frame defining the circumference of a contaminant chamber. If the filter paper is to be replaced with a new strip, the chambers are separated so that the band can be moved to place a new stretch of filter paper into the chamber, the frame then being lowered against the filter paper. The material to be filtered is supplied under pressure into the contaminant chamber, the seal against escape of contaminant being obtained by application of substantial pressure of the edge of the upper filter chamber, formed by the frame, against the filter material itself.